In the various operations which are carried out in steel making and coking plants and, more generally, in metallurgical plants, there are generated polluted air and gases of varying compositions. Most of these gases are laden with pollutants which must be completely removed or at least partly removed before the gases can be discharged into the environment, i.e. the ambient atmosphere.
Although some of these pollutants may be solids or gases which can conceivably be recycled in an industrial process, their concentrations are often too low to make recycling operations financially attractive.
For example, combustion gases are generated during the steel-making process and contain, in addition to nitrogen, carbon dioxide, oxygen and carbon monoxide. The carbon monoxide is a gaseous fuel which frequently is not convenient to recover because the concentration of the carbon monoxide varies widely during the steel making process. As a result only limited amounts of such exhaust gases are worthwhile reusing directly although they may be used to recover sensible heat. On the other hand, the combustible content of such gases, if simply scrubbed or otherwise treated to be freed of their pollutants, are lost and adversely effect the thermal balance of the system.
In addition, the air in steel making plants sporadically becomes laden with dust and gases which contain no components which are reusable economically and thus only pollutants. For example, in the production of slag sand or slag wool, in which molten blast furnace slag is treated with water, steam and/or air, there is generated an atmosphere which is latent with hydrogen sulfide and slag-wool particles which are of unpleasant odor and cause difficulties in breathing. These gases are detrimental both to the environment and to the worker in the plant. Dust-laden gases also are generated during the tapping of blast furnaces, the descaling of steel sheet, the flame-drying of freshly prepared ladles, the metallurgical treatment of pig iron or steel in ladles etc.
Coking plants produce steam during the charging of the coke ovens and during the quenching of the coke. The steam which is thus evolved and constitutes one of the gases which are treated in accordance with the present invention, contains dust and coking gases. This contaminated gas cannot be reused technologically and is difficult to clean.
As a result of the varied compositions of the various contaminated gases which are generated in a steel making plant and/or a coking plant or, more generally, in metallurgical operations, there is the need to provide a multitude of cleaning devices operating under varying principles and with sophisticated hardware in any plant of a considerable size.
For example, in some cases it is necessary to provide special burners to burn off the carbon monoxide generated in steel making processes and contained in flue gases. When the combustion is not adequate, it is necessary to use dry or wet filtration or to run the flue gases through sophisticated scrubbing columns.